Split 1x3x4 (Polished)

I was not super happy with [original RyanPuzzle's design](https://www.thingiverse.com/thing:2358453) because it was:
- too loose (huge tolerance)
- too catchy (sharp corners)
- consist of pieces of 2 differen things with different scale (unclear how to print)
- Screw mechanism is not well designed

All credits still go to RyanPuzzle, consider this thing as just a polished version of his puzzle.

In this design I used 20mm blocks (vs 19mm in the original Rubik's Cube) - this is just for e